In order to manufacture semiconductor devices, film formation and pattern etching are repeatedly applied to a semiconductor wafer. As semiconductor devices are becoming more and more highly miniaturized and integrated, demands on film formation have become stricter. For example, very thin insulating films, such as capacitor insulating films and gate insulating films are required to be even thinner and to achieve a higher insulation performance.
Conventionally, silicon oxide films and silicon nitride films are used as the insulating films. In recent years, however, it has been proposed to form the insulating films from materials having even higher insulating properties, such as a metal oxide, e.g., tantalum oxide (Ta2O5). A metal oxide film of this kind can be deposited by means of MOCVD (Metal Organic Chemical Vapor Deposition), i.e., using a vaporized metal organic compound. To form a tantalum oxide film by means of MOCVD, a metal alkoxide of tantalum, such as Ta(OC2H5)5 (pentoethoxytantalum: PET) is used as a raw material liquid.
The metal oxide film has an insulation property of high reliability even with a small thickness, and can further have a higher insulation property by means of a reformation process performed after the film deposition (Jpn. Pat. Appln. KOKAI Publication No. 2-283022). Conventionally, a tantalum oxide film used as an insulating metal oxide film is formed by the following method.
Specifically, a tantalum oxide (Ta2O5) film is first deposited on a semiconductor wafer to a predetermined thickness, in a CVD apparatus. For this, the raw material liquid is made to bubble to be in a gaseous state by e.g., nitrogen gas, or vaporized by a vaporizer set at a vaporizing temperature, and is supplied to a process chamber preset to have a vacuum atmosphere. At the same time, an oxidizing gas, such as oxygen, is supplied to the process chamber. The supplied raw material is decomposed to offer a film forming material on the surface of a wafer heated to a process temperature of from about 400 to 500° C. With this film forming material, a tantalum oxide (Ta2O5) film is formed on the surface of the wafer by means of deposition.
Then, the wafer is transferred into to a reforming apparatus and the tantalum oxide film is reformed in this apparatus. In the case of a UV ozone process, the wafer W is placed in an atmosphere containing ozone (O3), and UV rays emitted from a UV lamp are radiated onto the ozone above the surface of the wafer W. With the reformation process, the energy of the UV rays and activated oxygen atoms cause organic impurities, such as C—C bonds and hydrocarbon, contained in the tantalum oxide film to be cut and dissociated therefrom, thereby reforming the tantalum oxide film. The reformation process temperature is set at, e.g., about 600° C.
Then, the wafer is transferred to a heat-processing apparatus and the tantalum oxide film is crystallized in this apparatus. In this process, an atmosphere containing oxygen gas, and a process temperature, e.g., not lower than 750° C., which is higher than the crystallization temperature of tantalum oxide, are used. With this crystallization annealing process, the tantalum oxide film is compacted in a molecular level, and is planarly uniformed in the film thickness, thereby providing an insulating film having a good insulating property.
On the other hand, in manufacture of semiconductor devices, an increase in throughput is an important object in order to increase the mass productivity. Furthermore, as the cost necessary for maintaining heat-processing apparatuses is very high, it is required to reduce the number of apparatuses to be installed as much as possible. Under the circumstances, it has been proposed to perform the deposition and reformation described above in a single process chamber (Jpn. Pat. Appln. KOKAI Publication Nos. 9-153491 and 10-182300). In this case, however, since there is a substantial difference in process temperature between the deposition and reformation, byproduct films having stuck to the inner surface of the process chamber during deposition likely peel off due to the process temperature difference, and produce floating particles. Particularly, in an apparatus of the type supplying a process gas from a showerhead, byproduct films sticking to the surface of the showerhead easily peel off due to the process temperature difference.
In light of throughput and cost, it is preferable to also perform the crystallization in addition to the deposition and reformation in the same process chamber. However, since the process temperature of the crystallization is still higher than those of the deposition and reformation, the problem described above becomes more prominent and thus hinders this idea from being put into practice.